That's not at all why grid timing is so precise.

Multiple generation systems feed into the same grid. If they're out of phase by even a few milliseconds, that translates to huge power losses. If power generation companies didn't synchronize to high precision, they would lose a lot of power and probably break some equipment.

Equipment being out of phase has nothing to do with the timing. The timing of the 50/60 Hz signal actually changes throughout the day. On average the signal over 24 hours will equal about 24 hours so you can keep time with it, but as the load changes on the grid it will actually slow down and then speed back up when people turn off their devices at night.

The phases of the grid as a whole actually get synched up automatically. For example when they spin up a new turbine at a power plant if it is not within a certain percentage of the phase cycle it can actually cause massive amounts of damage as it gets pulled into the phase automatically.

The electric grid companies actually want to lower the current requirements for the 50/60 Hz cycle to be accurate in a 24 hour period to longer, such as possibly a week. This could mean that the clock in your oven for example may be a minute or two slow and slowly catch up over time as the grid has moments where it is clocked faster than 50/60 Hz.

For example see this graph of the last 60 minutes: http://www.nationalgrid.com/uk/Electricity/Data/Realtime/Fre... and here it is in real time for the whole US: http://fnetpublic.utk.edu/gradientmap.html

And here is the experiment that the power companies wanted to run/still are running regarding the relaxing of keeping the grid at 60 Hz: http://www.nbcnews.com/id/43532031/ns/technology_and_science...

For reference, the specification for the European power grid is in the "Continental Europe Operation Handbook", Part "P1, Load-Frequency Control and Performance".

https://www.entsoe.eu/publications/system-operations-reports...

It's actually a pretty elaborate system (who would have guessed?) with phase-stiffness between subsystems specified, because this basically defines the amount of power drawn/sourced. Timing is just the "outermost" regulation loop.

> as the load changes on the grid it will actually slow down and then speed back up when people turn off their devices at night.

When I sailed on ships we knew not to use alarm clocks that plug into an outlet, because the load on the ship's generators is always changing, thus making plug-in alarm clocks less dependable than wrist watches.

This is also the reason why a lot of clocks like that won't work on inverters that convert 12 VDC to 120 VAC since any load and most of them fall below spec.

> On average the signal over 24 hours will equal about 24 hours so you can keep time with it, but as the load changes on the grid it will actually slow down and then speed back up when people turn off their devices at night.

Yes, the load changes the frequency over the course of a day. In Great-Britain there's even a special peak after the afternoon TV shows finishes and people start turning on their electric kettles to prepare tea.

http://www.bbc.co.uk/britainfromabove/stories/people/teatime...

In fact, the exact frequency of the power grid can be used to identify precisely the time of the day!

http://en.wikipedia.org/wiki/Electrical_network_frequency_an...

That is really cool that they can use it as a sort of fingerprint!

I've heard otherwise elsewhere: that grid frequency was initially imprecise, was made precise to enable synchronous electric clocks, and then grid interconnection became feasible. https://en.wikipedia.org/wiki/Telechron#Henry_Warren:_the_Sy... , for instance.

I can't immediately find a cite for the story that some enterprising electric clock company would give clocks to execs at power companies, then let them get annoyed at large errors and demand stable frequency, but that's surely too good to need a cite, eh?

(edit: initially imprecise)

Grid interconnection has always been possible, whether it is precise or not, however if one grid was running faster than the other doing such an interconnect would cause the grids to eventually stabilise somewhere in the middle as the faster grid caused the slower grid to speed up and the slower grid caused the faster grid to slow down.

The amount of power wasted is insane though. Bringing new turbines online for example means getting the turbine to run in sync with the current clock cycle within a certain percentage otherwise massive damage can be done as the turbine jumps backwards or forwards when connected to the grid.

Yes, they do synchronize and yes, the number of cycles averaged over a day cycle is kept close to constant but: the frequency still floats. In fact, it floats enough to produce a unique "background hum fingerprint" which can be used to verify authenticity of audio recordings: http://www.bbc.co.uk/news/science-environment-20629671

I have a textbook somewhere that said the adjustments were due to so many things relying on it for syntonisation. I'm not in a position to dig it up and find a proper reference unfortunately.